The present invention relates generally to resource allocation in wireless hybrid time division multiple access/code division multiple access communication systems. More specifically, the invention relates to assigning uplink and downlink timeslots in such systems.
FIG. 1 depicts a wireless communication system. The system has a plurality of base stations 301-3011. Each base station 301 communicates with user equipments (UEs) 321, 323, 324 in its operating area or cell. Communications transmitted from the base station 301 to the UE 321 are referred to as downlink communications and communications transmitted from the UE 321 to the base station 301 are referred to as uplink communications.
In addition to communicating over different frequency spectrums, spread spectrum code division multiple access (CDMA) systems carry multiple communications over the same spectrum. The multiple signals are distinguished by their respective chip codes (codes). To more efficiently use the spread spectrum, some hybrid time division multiple access (TDMA)/CDMA systems as illustrated in FIG. 2 use repeating frames 34 divided into a number of timeslots 361-36n such as fifteen timeslots. In time division duplex (TDD) systems using CDMA, a timeslot is used either solely for downlink or uplink communications in a cell. In such systems, a communication is sent in selected timeslots 361-36n using selected codes. Accordingly, one frame 34 is capable of carrying multiple communications distinguished by both timeslot 361-36n and code. The use of a single code in a single timeslot with a spreading factor of sixteen is referred to as a resource unit. Based on a communication's bandwidth requirements, one or multiple resource units may be assigned to a communication.
One problem in such systems is cross cell interference as illustrated in FIG. 3. A second cell's base station 302 sends a downlink communication 40 to a second cell's UE 322 in a certain timeslot. In the same timeslot, an uplink communication 38 is sent from a first cell's UE 321. The uplink communication 38 may be received by the first cell's base station 301 at an unacceptable interference level. Although the second cell's base station 302 is further away than the first cell's UE 321, the higher effective isotopically radiate power (EIPR) of the second cell's base station 302 may result in unacceptable interference at the first cell's base station 301.
Also shown in FIG. 3 is cross interference between UEs 321, 322. An uplink signal 38 from a first cell's UE 321 will create unacceptable levels of interference to a downlink communication 40 in the same timeslot received by the second cell's UE 322, due to their close proximity.
Accordingly, there exists a need for reducing cross cell interference.